fix(cache): disable service worker to prevent stale cache on mobile

Flutter's PWA service worker caches the entire app shell aggressively,
causing users to see old versions even after deploys. Disabling it lets
nginx cache headers take effect. Also unregisters any existing service
worker already installed on user devices.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Dockerfile

@@ -6,7 +6,7 @@ COPY pubspec.yaml pubspec.lock ./
 RUN flutter pub get
 
 COPY . .
-RUN flutter build web --release --base-href /
+RUN flutter build web --release --base-href / --pwa-strategy=none
 
 # Stage 2: Serve with nginx
 FROM nginx:alpine

web/index.html

@@ -89,6 +89,15 @@
     });
   </script>
 
+  <script>
+    // Unregister any previously installed service worker so stale cache is cleared
+    if ('serviceWorker' in navigator) {
+      navigator.serviceWorker.getRegistrations().then(function(regs) {
+        regs.forEach(function(r) { r.unregister(); });
+      });
+    }
+  </script>
+
   <script>
     // Force cache busting: append build timestamp so stale JS/CSS is never reused
     var _v = new Date().getTime();